Variable speed transmissions have been in use for many years. Typically such a transmission will use two pulleys each having opposing wheelfaces and an endless member such as a chain or a rubber belt that engages the wheelfaces. The wheelfaces can be moved apart or together to very the radial location of the belt or chain on the wheelfaces.
One such variable speed transmission uses a metal chain containing packages of slats, which engage themselves in grooved wheelfaces and thus effectively provide a variable pitch all metal chain. This chain positions itself and establishes a pitch radius in the wheelfaces depending upon the opening between the wheelfaces. If the wheelfaces are moved close together, the chain rides out near the top of the wheelfaces and establishes itself with a relatively large pitch diameter. If the wheel faces are moved apart, the chain rides down near the center of the wheelfaces, establishing a relatively small pitch diameter. The resultant speed relationship between the variable speed shaft of the unit and the constant speed shaft of the unit is a function of the ratio of the pitch diameters of the chain at the variable speed grooved wheels and the constant speed grooved wheels.
Control levers and a control screw are provided to permit the wheelfaces to be adjusted in and out to an infinite number of positions and thus an infinite number of pitch diameter ratios can be established. This means that the transmission is infinitely adjustable from maximum rated speed down to minimum rated speed. The unit can be set to operate at any speed setting between the maximum and minimum speed ratings.
In the past such a variable speed transmission has been coupled to a bevel gear differential which has increased the accuracy of the basic pulley and belt or chain combination. However, even this combination does not provide sufficient accuracy for many applications. In addition, such a resulting combination is fairly complex.
The present invention overcomes these problems and offers numerous advantages over previous variable speed transmissions. With this invention it is possible to provide very narrow output speed regulation with very high accuracy. This invention essentially has zero backlash which is not possible with previous variable speed transmissions and hence the new variable speed transmission has very superior output accuracy. The present invention is also more compact and lighter in weight than previous variable speed transmission combinations and it offers greater ease in manufacturing, servicing and repair. The present invention's precision performance characteristics are ideal for accurate and precise control and provide a variable speed transmission that is readily adaptable for use in a variety of applications.